1. Field of the Invention
This invention relates to improvements in a cylinder direct injection spark-ignition engine in which fuel (such as gasoline) is directly injected into a cylinder, and more particularly to the improvements for achieving effective stratified charge combustion in such an engine.
2. Description of the Prior Art
Cylinder direct injection spark-ignition engines for an automotive vehicle have been proposed and put into practical use, in which fuel is directly injected into an engine cylinder to be ignited by a spark plug. One of them is disclosed in U.S. Pat. No. 5,553,588 entitled "Spark-ignited Direct Cylinder Fuel Injection Engine" and configured as follows: The engine has two intake ports for each cylinder, in which one of the ports is provided with a swirl control valve. Additionally, a piston is formed at its piston crown with a cavity forming part of a combustion chamber. Upon closing the swirl control valve, intake air is introduced into the combustion chamber through the other intake port thereby generating gas flow in the combustion chamber. In compression stroke, fuel is injected into the cavity thereby locally forming a layer of air-fuel mixture around the spark plug thus achieving stratified charge combustion.
Now, in the cylinder direct injection spark-ignition engines, it is required to carry the layered air-fuel mixture to the vicinity of the spark plug at a spark timing for obtaining a good heat generation timing.
However, in the above-discussed conventional cylinder direct injection spark-ignition engine, the gas flow in the combustion chamber is formed under the effect of the intake port which is directed outwardly or toward the periphery of the cylinder bore relative to a vertical cross flow plane, and therefore the gas flow is formed along the periphery of the cylinder bore regardless of presence or absence of the cavity formed at the piston crown. Accordingly, in order to smoothly accomplishing vaporization and transportation of air-fuel mixture for enabling lean air-fuel mixture combustion, control using a separate control factor becomes necessary thus complicating the configuration of the combustion chamber and control of the engine.